1/*
2 *  Copyright (c) 2014 The WebM project authors. All Rights Reserved.
3 *
4 *  Use of this source code is governed by a BSD-style license
5 *  that can be found in the LICENSE file in the root of the source
6 *  tree. An additional intellectual property rights grant can be found
7 *  in the file PATENTS.  All contributing project authors may
8 *  be found in the AUTHORS file in the root of the source tree.
9 */
10#include <stdlib.h>
11
12#include "vpx/vpx_integer.h"
13#include "vpx_ports/system_state.h"
14
15static int horizontal_filter(const uint8_t *s) {
16  return (s[1] - s[-2]) * 2 + (s[-1] - s[0]) * 6;
17}
18
19static int vertical_filter(const uint8_t *s, int p) {
20  return (s[p] - s[-2 * p]) * 2 + (s[-p] - s[0]) * 6;
21}
22
23static int variance(int sum, int sum_squared, int size) {
24  return sum_squared / size - (sum / size) * (sum / size);
25}
26// Calculate a blockiness level for a vertical block edge.
27// This function returns a new blockiness metric that's defined as
28
29//              p0 p1 p2 p3
30//              q0 q1 q2 q3
31// block edge ->
32//              r0 r1 r2 r3
33//              s0 s1 s2 s3
34
35// blockiness =  p0*-2+q0*6+r0*-6+s0*2 +
36//               p1*-2+q1*6+r1*-6+s1*2 +
37//               p2*-2+q2*6+r2*-6+s2*2 +
38//               p3*-2+q3*6+r3*-6+s3*2 ;
39
40// reconstructed_blockiness = abs(blockiness from reconstructed buffer -
41//                                blockiness from source buffer,0)
42//
43// I make the assumption that flat blocks are much more visible than high
44// contrast blocks. As such, I scale the result of the blockiness calc
45// by dividing the blockiness by the variance of the pixels on either side
46// of the edge as follows:
47// var_0 = (q0^2+q1^2+q2^2+q3^2) - ((q0 + q1 + q2 + q3) / 4 )^2
48// var_1 = (r0^2+r1^2+r2^2+r3^2) - ((r0 + r1 + r2 + r3) / 4 )^2
49// The returned blockiness is the scaled value
50// Reconstructed blockiness / ( 1 + var_0 + var_1 ) ;
51static int blockiness_vertical(const uint8_t *s, int sp, const uint8_t *r,
52                               int rp, int size) {
53  int s_blockiness = 0;
54  int r_blockiness = 0;
55  int sum_0 = 0;
56  int sum_sq_0 = 0;
57  int sum_1 = 0;
58  int sum_sq_1 = 0;
59  int i;
60  int var_0;
61  int var_1;
62  for (i = 0; i < size; ++i, s += sp, r += rp) {
63    s_blockiness += horizontal_filter(s);
64    r_blockiness += horizontal_filter(r);
65    sum_0 += s[0];
66    sum_sq_0 += s[0]*s[0];
67    sum_1 += s[-1];
68    sum_sq_1 += s[-1]*s[-1];
69  }
70  var_0 = variance(sum_0, sum_sq_0, size);
71  var_1 = variance(sum_1, sum_sq_1, size);
72  r_blockiness = abs(r_blockiness);
73  s_blockiness = abs(s_blockiness);
74
75  if (r_blockiness > s_blockiness)
76    return (r_blockiness - s_blockiness) / (1 + var_0 + var_1);
77  else
78    return 0;
79}
80
81// Calculate a blockiness level for a horizontal block edge
82// same as above.
83static int blockiness_horizontal(const uint8_t *s, int sp, const uint8_t *r,
84                                 int rp, int size) {
85  int s_blockiness = 0;
86  int r_blockiness = 0;
87  int sum_0 = 0;
88  int sum_sq_0 = 0;
89  int sum_1 = 0;
90  int sum_sq_1 = 0;
91  int i;
92  int var_0;
93  int var_1;
94  for (i = 0; i < size; ++i, ++s, ++r) {
95    s_blockiness += vertical_filter(s, sp);
96    r_blockiness += vertical_filter(r, rp);
97    sum_0 += s[0];
98    sum_sq_0 += s[0] * s[0];
99    sum_1 += s[-sp];
100    sum_sq_1 += s[-sp] * s[-sp];
101  }
102  var_0 = variance(sum_0, sum_sq_0, size);
103  var_1 = variance(sum_1, sum_sq_1, size);
104  r_blockiness = abs(r_blockiness);
105  s_blockiness = abs(s_blockiness);
106
107  if (r_blockiness > s_blockiness)
108    return (r_blockiness - s_blockiness) / (1 + var_0 + var_1);
109  else
110    return 0;
111}
112
113// This function returns the blockiness for the entire frame currently by
114// looking at all borders in steps of 4.
115double vp9_get_blockiness(const uint8_t *img1, int img1_pitch,
116                          const uint8_t *img2, int img2_pitch,
117                          int width, int height) {
118  double blockiness = 0;
119  int i, j;
120  vpx_clear_system_state();
121  for (i = 0; i < height; i += 4, img1 += img1_pitch * 4,
122       img2 += img2_pitch * 4) {
123    for (j = 0; j < width; j += 4) {
124      if (i > 0 && i < height && j > 0 && j < width) {
125        blockiness += blockiness_vertical(img1 + j, img1_pitch,
126                                          img2 + j, img2_pitch, 4);
127        blockiness += blockiness_horizontal(img1 + j, img1_pitch,
128                                            img2 + j, img2_pitch, 4);
129      }
130    }
131  }
132  blockiness /= width * height / 16;
133  return blockiness;
134}
135